Chevrolet 70 1969 Series, Shop Manual

Page: 57 / 913

CAB A N D BO DY MOUNTINGS 1-30
3. Separate the defroster air duct tubes from
air distributor.
4. Disconnect electrical wiring from heater
speed control resistor and from blower motor.
Resistor is located at top of blower scroll.
5.
Remove screws which attach the air dis­
tributor to cowl and to blower scroll. Remove air
distributor.
6. To remove the heater core and blower unit
as an assembly, remove the screws which attach
the heater core housing to the outside air inlet
duct. Carefully lower heater unit and remove from
compartment.
7. To remove the outside air inlet duct, re­
move screws which attach duct to firewall and in­
strument panel, then remove duct and seal gasket.
8. Remove screws which attach heater core
in housing. Remove core.
9. Remove screws which attach blower motor
to scroll. Remove motor and blower fan assembly.
N O T E : The heater core can be repaired by a
competent radiator core repairman.
IN S T A L L A T IO N (Refer to Fig. 30)
Assemble and install the heater components
in reverse of "Removal" procedures using new
gaskets and seals where necessary.
IM P O R T A N T : When connecting heater hoses
to core piping make sure the
5 /8
inch I.D. hose is
connected to small core pipe and that 3/4 inch I.D.
hose is connected to larger pipe.
If hoses are not installed as directed, poor
heat output and/or a ruptured heater core may re­
sult. The core, internally, is designed to accept
the higher pressure at the inlet (5/8 inch I.D . pipe)
side of core only.
HEAVY DUTY AIR-FLOW HEATER
The heavy duty air-flow heater operates on
full outside air and has a three lever control panel
and a blower motor control switch on dash (fig. 31).
Temperature control is by means of the air-
mix method; mixing heated outside air which has
passed through the heater core and outside air
which has by-passed the core in proportions nec­
essary to provide the desired temperature. The
control on dash for this purpose is marked " T E M P ."
With lever to the left, all the incoming air by­
passes the heater core. With lever to the far right,
all outside air must pass through the core, thus
providing maximum heat. When lever is positioned
part way, part tempered and part untempered air
passes through the heater.
The control on dash marked "A IR " regulates
the flow of outside air which passes through the
heater and into cab. This control must be posi­
tioned all the way towards the right in order to
obtain heat.
IM P O R T A N T : Do not operate the blower motor
when "A IR " control lever is in the full left position.
The heater fan speed is controlled by moving blow­
er switch lever from left to right positions "OFF-
LOW - SPEED, M E D IU M SPEED - and HIGH S P E E D .”
The " D E F R O S T " lever controls flow of air
to the windshield defroster ducts. With knob all
the way to the right, entire heater output is divert­
ed to the defroster ducts for defrosting.
For warm weather ventilation, place " D E ­
F R O S T ” and " T E M P ." control knobs in extreme
left positions, move "A IR " knob to extreme right,
then place fan switch lever to desired fan speed
position. The fan speed control resistor unit is
attached to the blower shroud with two screws. If
resistor should become defective, the result will
be high speed blower motor operation with blower
switch lever in both the " L O W " and "M E D I U M "
speed positions.
HEATER UNIT REPLACEMENT
(HEAVY DUTY AIR-FLOW TYPE)
(Refer to Figure
31)
R E M O V A L
1. Drain cooling system to just below level
of
heater core.
2. Mark hoses for identification then discon­
nect hoses at heater core fittings.
3. At front side of cowl, remove single bolt
which attaches the heater blower bracket to cowl.
4. At rear side of heater core housing, re­
move the small spring-type retaining washer from
" T E M P " control lever then remove the control wire
clamp screw. Pull wire from lever.
5. At top of blower motor, disconnect the
"A IR ” control wire in same manner.
6. Disconnect the blower adapter-to-air dis­
tributor hose.
7. At top of blower housing, near the cowl,
separate the wiring connection at the blower speed
control resistor.
8. Separate wiring connector at rear of blower
motor. Pull rearward on connection.
9. Underneath the dash, at right side of core,
remove four bolts which attach heater unit to cowl
extension.
10. Remove single bolt which attaches heater
support bracket to bottom of dash panel. This same
bolt attaches the blower motor ground wire.
11. Using care not to damage heater unit, work
the unit rearward and down from compartment.
12. If desired, the unit can be readily dis­
assembled for inspection or replacement of the
blower, motor, core, etc.
CHEVROLET SERIES 70-80 H EAVY DUTY TRUCK SH O P M AN U AL